In the forming of vehicle tires, it is desirable that the tire side wall be free of any radially projected rubber pins, impressions, depressions or other surface irregularities. The forming of the pins or needles is usually the result of the uncured tire band, in the final forming operation of the tire, being forced into the air release vents or passages which have terminal ends open to the inner surface of the tire forming cavity of the mold. For economical purposes, the pins are not removed and thus give to the tire an unfinished or hairy appearance.
Attempts to avoid surface irregularities on the tire side wall have been made particularly with regard to avoiding the necessity and resultant expense of removing the rubber pins from the finished tire. One attempt to eliminate the rubber pins is shown in British Pat. No. 922,788, issued Apr. 3, 1963, wherein a valve body is movably mounted in a vent for movement to a vent closing position by the expanding of the tire band against the cavity side wall. The valve is not movable to a full open position and is apparently limited in operation for use in horizontally extended vents so that the depression made by the valve is formed in the tread of the tire so as to appear as part of the tread.
In U.S. Pat. No. 4,021,168, bent nails having one or more washers positioned between the nail head and the face of the mold are inserted into the vents or passages of the tire mold. The uncured rubber is prevented from forming in the vents during a molding operation and air is permitted to escape. However, the nail head and washer assembly form depressions over the entire tread and tire side wall surface.
In U.S. Pat. No. 3,377,662, a plug means is inserted within an air vent with the plug having a plurality of small vent holes so that any rubber protruded in the air vent would not generate undesirable projections on the finished surface of the tire. Additionally, the plug means is adapted to be removed from an air vent for cleaning purposes.
In U.S. Pat. No. 3,842,150, the release of air from the mold cavity through vents is controlled by valves that are actuated in response to a selective application of pressure thereon. Although the control valve functions satisfactorily to form a tire having a smooth side wall, appreciable time and resultant expense is involved in the manufacture of the control valves and in the control system for synchronizing the flow of variable pressure air through the valves with the steps in the tire forming operation. The valve unit for the tire mold in U.S. Pat. No. 4,492,554 is engaged and moved by an expanding tire band to a vent closing position to form a smooth surface continuous with the inner surface of the tire cavity and is yieldably urged to a vent opening position by a spring means. Although the valve unit of U.S. Pat. No. 4,492,554 is economically more acceptable than the valve unit of U.S. Pat. No. 3,842,150, frequent cleaning is required to insure their proper operation resulting in down time loses of the molding equipment.